Aico Comprehensive Guide to Smoke Alarms: Features, Installation, and Radio Link Systems

AUDIBILITY

Audibility is another factor to be considered. The Code comments that ideally, an alarm system should be capable of producing a sound level of 75dB(A) at the bedhead, but that this is unlikely to be achieved unless there is a sounder/smoke alarm in the bedroom itself. As there is no evidence of life being lost in single family dwellings due to the lower sound level achieved by siting an alarm within 3 metres of the bedroom doors, in many dwellings this would be acceptable. In HMOs, where higher levels of ambient noise is likely, additional alarms/sounders may be necessary.

A practical way to check audibility is with the alarm sounding in its intended location, check that the occupant is able to hear it in each bedroom with the door closed above the sound of a radio set to a reasonably loud conversation level. In this case, interconnected alarms provide an ideal solution, a remote alarm picking up the fire and a sounder being triggered to wake the occupier.

SPECIAL NEEDS

PROVISION

Back in 1995, the original Code acknowledged the special needs of people who are deaf or hearing impaired and recommended the use of alternative fire alarm systems to meet their needs. More attention is paid to the issue in the new 2004 update.

A special alarm can be incorporated into domestic mains fire alarm systems to protect people with impaired hearing. It’s a simple, yet ingenious idea.

In the event of a fire being detected, a small vibrating pad located beneath the sleeper’s pillow gently alerts them. At the same time a powerful strobe light flashes to provide a further visual warning.

Devices such as these are now increasingly cited as important considerations and should be considered as a matter of course in applications where the residents are likely to be elderly, as in a nursing home for example, or in sheltered accommodation.

The 2004 Code notes that the final system applied should take into account the assessed needs of the person being protected. However, it should always conform to BS 5446: Pt.3 (Grade A and B systems aside, where other standards quoted may be more appropriate).

INSTALLATION OF GRADE D AND E SYSTEMS

Once these considerations have all been taken into account and the system adequately planned, it can then be installed, tested and commissioned.

Systems should be installed in accordance with BS 7671 (IEE Regulations 16th Edition) by a qualified installer. All alarms should be fitted into place securely and permanently, and attention given to protecting all wiring from impact or rodent damage by recessing or trunking.

If you intend to install the alarms in a new building, however, it is usually necessary to wait until all other work on site has been completed and the building has been fully cleaned before installing any smoke alarms. This is because excess dust and debris from building work can contaminate the alarms and render them prone to false alarms. However, new ‘Easi- fit’ style alarms are a useful exception, with the wiring able to be completed during ‘first fix’ and the detector head simply slotted into place when all cleaning work has been completed.

If, for any reason, other types of alarms have to be installed before all work is complete, ensure that they are completely covered, particularly around

the edges, with the dust cover that should be supplied with each alarm. Only when all cleaning is finished should these dust covers be removed.

POWER SOURCE

The normal supply for Grade D and E systems is the public mains supply. A Grade D system should be connected either to an independent circuit at the dwelling’s main distribution board (with no other electrical equipment attached except for a dedicated monitoring device) or a separate, electrically protected, regularly used local lighting circuit. A Grade E system may only use the former option.

Hard wired interconnected smoke alarms should be on one final circuit. However, the 2004 version of the code now accepts that smoke and heat alarms using a radio signal for the interconnect can be separately wired from the nearest lighting circuit with a permanent mains supply.

RADIO LINKED SYSTEMS

Pages 41-44 of the 2004 Code now set out the criteria for radio-linked systems. It is acknowledged now that Grades D-F systems may use radio interconnection. However, it warns about the potential drawbacks of battery powered units being interconnected in such a way if there is a need to replace the batteries at regular intervals (by implication mains powered radio-linked alarms do not have these drawbacks).

As is typical with the Code, it stresses the need to ensure that such a system meets the needs of the application.

The new publication also goes out of its way to recognise that the old Code

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